This invention relates to the monitoring of synthetic textile yarns, and in particular to the monitoring of the interlace of an interlaced multifilament yarn, twist level in a twisted or cabled yarn or tension balance of a cabled yarn, hereinafter referred to as processed yarns.
Historically, mechanical techniques, e.g. by pin insertion and thickness measurement, for the determination of the presence of interlace nodes in an interlaced multifilament yarn, twist levels in a cabled or twisted yarn or tension balance in a cabled yarn have been used in a laboratory. To improve on those techniques, optical techniques have been used for the measurement of the profile variation in textured, drawn or POY yarns due to the presence of interlace or twist nodes. The use of such optical techniques is well established, including laser/photo diode, LED/photo diode and laser/charge coupled diode(CCD). These optical techniques offer substantial advantages over the mechanical techniques since optical techniques are not speed limited and require minimum contact with the yarn, i.e. only guides to locate the yarn in the sensing device. However, to date the optical techniques have not offered the levels of accuracy obtainable using conventional mechanical techniques in the laboratory, to such an extent that in many cases they are used only to establish whether interlacing or twist is present in the yarn but not to measure the level of such interlacing or twist. The particular problems of the optical techniques used to date are their insensitivity to both tension variation and profile changes in the yarn not associated with interlace nodes or twist. These problems are particularly pronounced in the case of fine denier POY or drawn yarns, for which profile variations due to interlace nodes or twist are very small. In addition, significant variations in response have been encountered with time from a particular sensor, and from sensor to sensor. These problems have resulted in poor accuracy even in a laboratory where good controls are possible, and in consequence it has been impracticable to use such techniques for on-line monitoring of the interlacing or twist of synthetic textile yarns.
It is an object of the present invention to provide a method of accurately measuring the interlace or twist level in a processed textile yarn which avoids or overcomes to a significant extent the problems described above in connection with conventional mechanical or optical techniques, and which can be used in a laboratory, at the process threadline, or for on-line monitoring.
The invention provides a method of monitoring the interlace or twists in a processed textile yarn, comprising forwarding the yarn past an optical transmitting and receiving device, recording the xe2x80x98originalxe2x80x99 signal emitted by the receiving device, and using cross-correlation, comparing the original signal with a signal to be expected from monitoring an ideally processed yarn to produce a processed signal indicating by its value the degree of matching of the original signal with the expected signal.
The method may comprise noting the amplitude of the processed signal relative to a pre-determined threshold value representing acceptable interlace or twist nodes in the processed yarn to give the number and distribution of nodes in the yarn. In addition, the method may comprise adjusting the threshold value in accordance with the desired strength of the nodes. The threshold value may be adjusted between 60% and 140% of a nominal value, which may be 1.
The expected signal may be devised by performing a frequency analysis on the original signal to establish a peak frequency. The peak frequency may be used to determine the distance between nodes in an ideally processed yarn and to construct the form of the expected signal.